1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, a fractional N-PLL circuit, an electronic apparatus, a moving object, and a determination method of a reference frequency of the fractional N-PLL circuit.
2. Related Art
An oscillator is known, in which a fractional N-PLL is connected to a rear stage of an oscillation circuit, and by changing a setting of a division ratio of the fractional N-PLL from an outer terminal, a plurality of frequencies can be output. In this type of oscillator, a fractional division ratio is determined such that a desired frequency which is obtained by fractionally dividing a reference frequency using a fractional N-PLL is obtained, but a frequency in which an integer value boundary spurious is generated is changed according to the fractional division ratio, and thus there is a case where phase noise or phase jitter of an oscillator is generated by an influence of the integer value boundary spurious, according to a relationship between a spurious frequency and an output frequency.
In contrast to this, in a frequency converter described in U.S. Pat. No. 8,305,115, an action is taken such that an integer value boundary spurious is not generated within a loop bandwidth, by switching two types of frequencies in order to use as a reference frequency of a fractional N-PLL.
However, there is a problem that, in a method described in U.S. Pat. No. 8,305,115, two resonators are required to generate two types of reference frequencies, and there are many factors that become an obstacle in miniaturization and cost reduction, thereby being negative in terms of reliability. In this way, in the related art, in a case where a plurality of frequencies are generated by a fractional N-PLL, there is a method for decreasing the integer value boundary spurious using a plurality of resonators (reference frequencies), but there is no method for enabling a plurality of frequencies to be output, while decreasing an influence of the integer value boundary spurious using one resonator (reference frequency).